1. Field of the invention
This invention relates generally to the field of access doors providing access to the interior of a duct, and specifically to an access door designed to provide easy access to the interior of grease ducts and other ducts serving, for example, commercial and institutional kitchens, allowing the cleaning, servicing and inspection of the ducts, or any wires, equipment, or other components located within the ductwork.
2. Prior Art
It often is desirable to have easy access to various different types of ductwork. For example, prior to the installation of the ductwork, it may necessary to install fire system equipment or nozzles and install or reset dampers on the interior of the ductwork. However, once the ductwork has been installed at a site, it may be advantageous to install these access panels after other mechanical and/or electrical equipment has been installed so that areas chosen for the installation of the access panels will least interfere with opening of the access panels and/or will be the best location based on intended use and application. Additionally, it may be difficult, if not impossible, to access the interior of the ductwork without cutting a hole in the ductwork or otherwise breaching the integrity of the duct wall after the ductwork has been installed. It especially is desirable to be able to access the interior of ductwork used as exhaust ducts so as to be able to remove any buildup on the interior surfaces of the duct wall.
For ductwork used as the exhaust or grease ducts serving commercial and institutional kitchens, flammable byproducts, such as grease, may attach to the interior surface of the ducts. This grease buildup often is flammable and grease fires within the exhaust ductwork can be a common occurrence. In order to clean and inspect or to maintain equipment which may possibly be located within the duct, various building and safety codes require a certain number of access ports in the ductwork in order to be able to both clean out the ductwork and to combat any grease fires which may occur in the ductwork. Historically, access ports generally were created by cutting out a portion of the ductwork or the duct wall so as to allow access to the interior of the duct, and then screwing or otherwise attaching a coverplate over the port. Such access ports often employ numerous fasteners which may require removal and replacement through the use of handtools. However, often such cut-and-cover access ports are not sufficiently well-built so as to survive a fire, that is, are not structurally safe, or to prevent flames from licking out from between the cover and the duct wall.
U.S. Pat. No. 4,913,127 to David E. Dugger, for a fire resistant duct access door for cooking equipment exhaust systems, discloses one apparatus for allowing access to the exhaust ductwork system for kitchen cooking equipment, particularly in commercial establishments. The Dugger access door comprises an access collar secured to the ductwork supporting a support shoulder. The support shoulder in turn allows the attachment of a seal means and the access door, which are releasably attached to the access collar. The Dugger access door suffers from several disadvantages. First, the access collar protrudes a relatively large distance from the ductwork surface, thus presenting a large, outwardly projecting profile. Therefore, the Dugger access door is not well-suited for applications having limited space around the ductwork. Secondly, the access collar presents additional surfaces on which grease or other contaminates can gather. Third, as the Dugger access door generally is welded to the ductwork, it presents certain dangers with respect to retrofitting the access door onto already used ductwork, as the welding process may ignite the grease which already has built-up on the inner surface of the ductwork.
A code effected in 1991 provides that only those doors listed by Underwriters Laboratories may contain or employ fasteners which penetrate the wall of the duct. For example, the access doors must pass certain penetration tests when exposed to flames. Therefore, a new generation of access doors is required and desirable both to comply with these new code sections and, at the same time, which can be installed on new ductwork or retrofitted on to existing ductwork without causing the fire hazard created by the welding process.